At the same time the 10.50 comes with inconvenient backstays which need to be changed with every tack and jibe while the 12.50 in comparison is nicely comfortable with no backstay.

Certainly no need to adjust on the tacks. The 10.50 does not have a square cut mainsail so the sail actually clears the backstays fine upwind. Downwind, perhaps something extra to deal with but most race boats have this issue anyways so it's not like it is unique to the 10.50. The rigging on the 12.50 is great in this sense and I would imagine at some point the 10.50 could go in this direction. Finot had a 10.50 customized and he took many of the approaches for the 12.50 (backstays, all winches forward and inside, etc) and applied them post production onto the 10.50.

As for the SF3200, there has been quite a bit of discussion on this boat here but I haven't seen anything from someone who actually owns one yet. I havent sailed one and have only sailed on the 32i and 35i Sun models.